In the past three decades, electricity has risen from 25% to 40% of end-use energy consumption in the United States. With this rising demand for power comes an increasingly critical requirement for highly reliable, high quality power. As power demands continue to grow, older urban electric power systems in particular are being pushed to the limit of performance, requiring new solutions.
Wire forms the basic building block of the world's electric power system, including transformers, transmission and distribution systems, and motors. The discovery of revolutionary HTS compounds in 1986 led to the development of a radically new type of wire for the power industry; this discovery is the most fundamental advance in wire technology in more than a century.
HTS wire offers best-in-class performance, carrying over one hundred times more current than conventional copper and aluminum conductors of the same physical dimension do. The superior power density of HTS wire will enable a new generation of power industry technologies. It offers major size, weight, and efficiency benefits. HTS technologies will drive down costs and increase the capacity and reliability of electric power systems in a variety of ways. For example, HTS wire is capable of transmitting two to five times more power through existing rights of way. This new cable will offer a powerful tool to improve the performance of power grids while reducing their environmental footprint. However, to date only short samples of the HTS-coated tape used in the manufacture of next-generation HTS wires have been fabricated at high performance levels. In order for HTS technology to become commercially viable for use in the power generation and distribution industry, it will be necessary to develop techniques for continuous, high-throughput production of HTS-coated tape.
MOCVD is a deposition process that shows promise for the high throughput necessary to cost-effectively produce HTS-coated tapes. During MOCVD, HTS film, such as yttrium-barium-copper-oxide (YBa2Cu3O7, or YBCO) may be deposited by vapor-phase precursors carried by an inert gas to a heated buffered metal substrate via chemical reactions that occur at the surface of the substrate.
Hubert, et al., U.S. Pat. No. 5,820,678, dated Oct. 13, 1998 and entitled “Solid Source MOCVD System,” describes a system for MOCVD fabrication of superconducting and non-superconducting oxide films that includes a delivery system for the feeding of metalorganic precursors for multi-component chemical vapor deposition. The precursors can be ground at a desired rate and fed to a vaporization zone and then to a reaction zone within a deposition chamber for thin film deposition. However, the throughput achievable by the process of Hubert et al. is greatly limited. The substrate upon which MOCVD occurs is fixedly attached, e.g., with a thermally conductive paste, to a substrate holder throughout the deposition process. As a result, discontinuous deposition runs characterize the MOCVD Hubert et al.'s process, which greatly limits the yields achievable through such a process.
Attempts have been made to increase the deposition efficiency of MOCVD processes. Tompa, U.S. Pat. No. 6,289,842, dated Sep. 18, 2001, and entitled “Plasma Enhanced Chemical Vapor Deposition System” discloses an rf plasma generating system to enhance the deposition process in a discontinuous wafer coating system. Hubert, et al., U.S. Pat. No. 5,820,678, provides coils connected to a 13.54 MHz generator wrapped around the injection cone of the vaporized reactants to produce an rf plasma and enhance the chemical reactions as the gas mixture arrives at the reaction zone within the deposition chamber.
P. C. Chou, et al., “Optimization of Jc of YBCO films prepared by photo-assisted MOCVD through statistical robust design,” Physica C 254 (1995) 93-112] discloses the achievement of a high deposition rate (one micron per minute) of yttrium-barium-copper-oxide (YBCO) film using photo-assisted CVD. Chou, et al. utilizes a diatomic oxygen atmosphere and a halogen lamp that emits a wide range of electromagnetic radiation (including both UV and infrared (IR) radiation) and relies upon the halogen lamp to heat the substrates (IR) as well as the precursors (UV) entering the deposition zone to enhance reaction kinetics, which often results in premature precursor decomposition. Chou, et al.'s process is neither scalable nor reproducible, and is not well suited to continuous deposition onto extended lengths of substrate; the research is therefore not compatible with a high-throughput MOCVD process.
Microwave plasma-enhanced chemical vapor deposition (PECVD) of yittrium-stabilized zirconia (YSZ) thin films research has been published by B. Preauchat et al., “Performances of microwave PECVD reactor or thin and thick oxide coatings at extremely high deposition rate”, Proceedings of the 8th International Plama Surface Engineering Conference, (2001)109-115). B. Preauchat et al's system includes a deposition chamber formed by walls of quartz. This requires high temperature glassware work and makes it difficult to construct a system for continuous deposition of long length wire.
A better approach to a large-scale MOCVD system utilizes a reel-to-reel spooling system that translates a plurality of buffered metal substrate tapes through an MOCVD chamber. The substrate tapes translate side by side, entering and exiting the MOCVD chamber through slits in the chamber walls, and undergo thin film deposition therein. A radiant substrate heater and a showerhead may be sized appropriately to create a large range of deposition zone areas so as to accommodate thin film deposition over a large zone onto the multiple translating substrate tapes. In addition to a large deposition zone, the other main factor that affects throughput is the thin film growth rate in the MOCVD process.
Complex reaction kinetics govern the thin film growth rate achievable in such a process to a great extent. Factors contributing to these complex reaction kinetics include the chamber pressure, the substrate temperature, the oxygen content and its method of introduction to the deposition zone, the amount of precursors being supplied to the deposition zone (determined by both the precursor molarity and the mass flow rate of the precursor vapors and their inert carrier gas through the showerhead assembly), the temperature at which the precursors are maintained prior to their introduction into the deposition zone, and the exhaust efficiency of the reaction byproducts away from the deposition zone.
It is therefore an object of the invention to provide an improved throughput continuous MOCVD system by enhancing reaction kinetics utilizing an energy source in the deposition zone.
It is therefore an object of the invention to provide an improved throughput continuous MOCVD system by enhancing reaction kinetics utilizing a UV or microwave energy source in the deposition zone.
It is therefore an object of the invention to provide an improved throughput continuous MOCVD system having enhanced utilization efficiency of precursors during the deposition of superconducting thin films.
It is another object of the invention to provide an improved throughput continuous MOCVD system by enhancing reaction kinetics by providing a monoatomic oxygen (O) atmosphere within the deposition zone,